Modulating boiler system

ABSTRACT

A modulating boiler system for heating a structure including a controller, a boiler operatively connected to the controller, and a thermostat operatively connected to the controller and boiler. The controller assesses a level of thermostat activity over a predetermined measuring period and adjusts the boiler in response to the level of activity to increase the boiler&#39;s efficiency.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.13/921,507, filed on Jun. 19, 2013, entitled “MODULATING BOILER SYSTEM”herein incorporated by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates generally to a modulating boiler system,and more particularly to a modulating boiler system in which energyinput to a boiler is reduced through the use of moving averages of theamount of time that the boiler's thermostat is on.

BACKGROUND OF THE INVENTION

Known boiler systems typically employ an outdoor sensor to assess thedifference between the outdoor ambient air temperature and thetemperature of the air inside a structure to be heated. The outdoorsensor responds to the outdoor air temperature to adjust the set pointtemperature of the boiler. The set point temperature is decreased inwarmer weather and in colder weather the set point is increased. Thistechnique is referred to as “outdoor reset.”

There are, however, limitations to using outdoor reset systems. Forexample, the outdoor sensor requires a puncture through the wall. Theoutdoor sensor must also be positioned such that it reflects the averagetemperature of the outside air around the structure to be heated.Significantly, the sensor must not be influenced by the sun's radiation,snow, ice, or other heat sources. Sensors must also be calibratedperiodically to ensure proper performance. Additionally, the “resetratio”, i.e., the change in boiler set point for a change in outdoortemperature must be programmed into the boiler control. Since there isno “feedback”, the reset ratio is typically set very conservatively toensure sufficient heat is available to maintain home comfort and theeffectiveness of the outdoor control to reduce energy consumption isseverely limited.

Furthermore, sources of heat gain or loss not related to outdoor airtemperature, e.g., open windows and heat generated by human occupation,are not captured by the sensor. Constraining the set point of a boilermay compromise comfort in systems where a minimum boiler watertemperature is necessary to ensure comfort. Finally, outdoor resetsystems cannot be used with fixed set point boilers.

In view of the above, outdoor reset sensors often obtain erroneousmeasurements of outdoor air temperature. If the outdoor air measurementis erroneous, the set point established for the boiler can result isinsufficient heat to satisfy the thermostat(s).

With the foregoing problems and concerns in mind, it is the generalobject of the present invention to provide a modulating boiler system inwhich the energy input to a boiler is reduced, and efficiency therebyincreased, without the limitations of an outdoor reset system or the useof an outdoor air sensor.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a modulating boilersystem with an increased efficiency.

It is an additional object of the present invention to provide amodulating boiler system that is capable of reducing energy input to aboiler to increase the boiler's efficiency.

It is a further object of the present invention to provide a modulatingboiler system that reduces energy input to a boiler to increase theboiler's efficiency without the drawbacks of known systems.

It is yet another object of the present invention to provide amodulating boiler system that reduces energy input of a boiler toincrease the boiler's efficiency without the need for an ambient airtemperature sensor.

It is an additional object of the present invention to provide amodulating boiler system that reduces energy input of a boiler toincrease the boiler's efficiency by the use of “feedback” to exploit thefull turn-down capability of a modulating boiler.

It is an additional object of the present invention to provide amodulating boiler system that reduces energy input of a boiler toincrease the boiler's efficiency through the use of moving averages ofthe amount of time that the boiler's thermostat is on.

This and other objectives of the present invention, and their preferredembodiments, shall become clear by consideration of the specification,claims and drawings taken as a whole.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a chart depicting a plot of boiler inputs achieved at multipleloads through use of a moving average algorithm of the presentmodulating boiler system.

FIG. 2 is a chart depicting use of an exponential moving average of thepresent invention to reduce boiler input in a multiple thermostatsetting.

FIG. 3 is a chart depicting a plot of boiler water temperatures achievedat multiple loads through use of a modulating boiler system of thepresent invention compared to a plot of boiler water temperaturesobtained through use of a system assessing outdoor air temperature.

FIG. 4 is a chart depicting a plot of boiler inputs achieved at multipleloads through the modulating boiler system of FIG. 3 compared to a plotof boiler inputs obtained through use of a system assessing outdoor airtemperature.

FIG. 5 is a simplified schematic diagram of a modulating boiler systemin accordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In order to maintain a thermostat-controlled space at a specifictemperature, the energy supplied, as measured over time, must exactlymatch the heat loss of the controlled space. If more energy is suppliedthan heat lost, the space will rise above the thermostat setting. Ifless energy is supplied, the thermostat temperature setting will not bereached. As described in greater detail below, the present systemdirectly determines the energy and heating needs of a space to increaseboiler efficiency to overcome the limitations of known systems.

The present system uses a moving average to calculate the “on-time” of athermostat over a specific measuring period to directly measure theenergy needs of a space. This moving average is used to adjust theboiler energy input to raise or lower the temperature of the boilerwater. For example, if the on-time of a thermostat is low over themeasuring period, i.e., the heat loss from the zone affected by thethermostat is low, the boiler input is reduced thereby causing areduction in the boiler water temperature. Moreover, the heat outputfrom hydronic baseboard elements is approximately linear with watertemperature. Thus, if the input energy from the boiler is reduced,equilibrium will occur at lower water temperature.

The reduced temperature of the boiler water results in a slower increasein room temperature and increases the on-time for the thermostat. Alonger thermostat on-time over the measuring period increases the movingaverage until a stable condition is achieved. Increasing boiler load dueto colder outdoor temperatures causes increases in thermostat cycles,boiler on-time, and thus the moving average. This “feedback” approachensures sufficient heat is always available.

As will be appreciated, this proportional control acts to increase thethermostat cycle time and thus the boiler on-time by reducing input tothe boiler during periods of reduced energy usage, with a consequentreduction in system losses, increased boiler efficiency and improvedcomfort.

This is shown in FIG. 1, which graphically illustrates a plot of energyinput 10 at various loads achieved through a moving average algorithm ofthe present invention. Load is represented on the x-axis and boilerenergy input on the y-axis. As depicted, the moving average of thepresent system results in reduced boiler energy input to a boiler atreduced boiler loads. For example, at a boiler load of approximately tenpercent 11, the boiler energy input is reduced to about thirty percent.As will be appreciated, the algorithm results in increased input as theboiler load is increased.

The moving average is an important aspect of the present invention. Bybasing calculations on thermostat on-time, as opposed to temperature,the present system does not require a sensor arranged to detect ambientair temperature. Further, the present system does not have the inherentlimitations of outdoor reset systems such as susceptibility to errorfrom outdoor heat sources, e.g., the sun, snow and ice. Moreover, giventhat the system of the present invention is wholly self-contained, allsources of energy gain/loss are reflected in thermostat cycling time. Inaddition, the present system ensures sufficient excess energy ismaintained to ensure that the thermostat zone can respond tounanticipated load changes.

In operation, when energy needs are low, the boiler acts as a smallermore efficient unit capable of achieving required temperatures withoutthe imposed constraints of an outdoor reset control. More specifically,the present system reduces the boiler water temperature on warmer daysso that the boiler is effectively “smaller” allowing the thermostat tobe satisfied with lower water temperatures than those required on colderdays.

The present system operates by sampling the thermostat state, either onor off, at a high enough rate to accurately capture all thermostatcycles. An exponential moving average (“EMA”) is then created for themeasuring period, which is preferably a one-hour interval. To improveaccuracy a second EMA is created using the initial EMA as input. Thevalue of the EMA is between 0 and 1. When a boiler start is demanded,the boiler energy input is determined by the EMA value multiplied by themaximum BTU set for the boiler. When more than one thermostat isconnected to the control, the highest EMA is chosen to determine energyinput.

This is shown in FIG. 2, which graphically illustrates how the presentsystem uses an EMA 13 to reduce boiler energy input in a multiplethermostat setting. The highest EMA 13 is chosen between multipleconnected thermostats, which ensures the zone with the greatest energyneed is satisfied. As depicted, the EMA 13 reduces boiler energy inputto approximately forty-eight percent at a twenty percent external load.

FIG. 3 graphically illustrates the efficacy of the inventive movingaverage system compared to a known outdoor reset system. The figuredepicts boiler load 12 on the x-axis and boiler water temperature 14 onthe y-axis. A plot of boiler water temperature 16 using the inventivemoving average system is juxtaposed with a plot of the boiler watertemperature 18 derived from an outside air system.

As will be appreciated, with an increasing load on the boiler, themoving average system functions to increase the boiler water temperaturein a similar fashion to the outdoor reset system. With the presentsystem, however, lower boiler water temperatures are attained resultingin higher efficiencies than possible with the outdoor reset system. Forexample, at a load of 0.2, is at about 132° F. with the moving averagesystem while the boiler water using the outdoor air system is at about142° F.

Likewise, FIG. 4 illustrates the benefits of the moving average systemcompared to a known outdoor reset system. In FIG. 4, boiler energy inputis represented on the y-axis and load on the x-axis. A plot of boilerenergy input 20 achieved through the inventive moving average system iscontrasted with boiler input 22 that results from use of an outdoorreset system. As shown, lower boiler energy input is possible with thepresent moving average system resulting in higher efficiencies thanpossible with the outdoor reset system. For example, at a load of 0.1,boiler energy input using the moving average system is about 0.3 or 30%.In contrast, with prior art outdoor reset systems, the boiler energyinput at this same load is about 0.5 or 50%.

It is therefore an important aspect of the present invention that thecontrol of the modulating boiler system described herein does notindirectly rely upon an outdoor ambient-air sensor. Rather, the presentinvention directly determines the energy and heating needs of anenclosure by determining the boiler's moving average of thermostaton-time for the enclosure. By directing sensing the on-time or cycles ofthe boiler, the control system of the present invention is capable ofaltering the input energy of the boiler itself so as to optimize thesize of the boiler (that is, the BTU output of the boiler), as well asresponding to the on-time thereof, thus increasing the overallefficiency of the system. The control system does not impose limitationson water temperature, thus allowing the instantaneous needs of thesystem to be satisfied.

Moreover, by directly controlling the size of the boiler, and byselectively controlling its time of operation per unit time, themodulating boiler system of the present invention will cause the boilerto experience less on/off cycles, thus reducing wear and tear on theboiler assembly, and reducing maintenance concerns correspondingly.

Referring now to FIG. 5, a preferred embodiment of a modulating boilersystem of the present invention is shown. The system includes acontroller 24 that is connected to a boiler 26 and a thermostat 28. Aswill be appreciated, the moving average algorithm of the presentinvention resides in, and is run by, software contained in thecontroller 24. The controller 24 receives data from the boiler 26regarding the temperature of the boiler water via a data link 30. Thecontroller 24 can also increase or decrease the temperature of theboiler water through a control link 32 depending upon thermostaton-time. As such, the controller 24, in addition to the boiler 26, isconnected to a thermostat 28 so that it may receive data regarding itson-time.

In use, the controller 24, via the inventive algorithm, creates anexponential moving average of thermostat on-time by measuring the timethe thermostat 28 is on over, for example, a one-hour period. Thecontroller 24 will then determine boiler input by multiplying theexponential moving average by the maximum BTU output of the boiler 26.After this determination has been made, the controller 24 will typicallyalter the boiler input either increasing or decreasing the watertemperature of the boiler 26.

Those skilled in the art will appreciate that the present invention isnot limited to the embodiments described, but that various modificationsand alterations can be made without departing from the scope of thepresent invention.

I claim:
 1. A method of increasing boiler efficiency comprising thesteps of: assessing an activity level of at least one thermostat over apredetermined time period, said at least one thermostat being inoperative connection with a boiler; and adjusting said boiler inresponse to said activity level of said thermostat.
 2. The method ofclaim 1 wherein said activity level is an exponential moving average ofan amount of time said at least one thermostat is on during saidpredetermined time period.
 3. The method of claim 2 wherein said boileris adjusted by regulating energy input to said boiler.
 4. The method ofclaim 3 comprising the additional step of: determining an appropriateenergy input to said boiler by multiplying said exponential movingaverage by a maximum BTU for said boiler.
 5. The method of claim 2wherein said at least one thermostat is two or more thermostats and anexponential moving average is created for each of said two or morethermostats.
 6. The method of claim 5 comprising the additional step of:selecting a highest exponential moving average from said exponentialmoving averages for said two or more thermostats.
 7. The method of claim6 wherein said boiler is adjusted in response to said highestexponential moving average.